(1) Field of the Invention
The present invention relates to a subscriber line radio concentration system. More particularly, it relates to a subscriber line radio concentration system (in other words, a multiple access radiotelephone system) having an automatic response unit suitable for a loop back test pertaining to a transmission test of access lines from a master station (servicing switching center) to a user (subscriber) terminal equipment.
(2) Description of the Related Art
In the multiple access radiotelephone system, both the master station and the subscriber terminal station cannot be constantly supervised by maintenance personnel. Therefore, to determine whether or not the communication channel between the master station and the subscriber terminal station is defective, it is desirable that a loop back test be carried out automatically.
In the conventional loop back test, however, it is necessary for someone such as a maintenance engineer to be in attendance at the called subscriber terminal station. Such personal attendance is necessary because, when a call is effected from a master station to a subscriber terminal station, the connection of the communication channel between the calling master station and the called subscriber terminal station is acknowledged only when an individual, in response to a ringing tone at the called subscriber terminal station, lifts the handset of the telephone set and responds to the call. Therefore, conventionally, a fully automatic loop back test cannot be carried out.